The objective of this proposal is to understand the nature and functions of the transforming genes of avian sarcoma viruses (ASVs) and their normal cellular counter-part proto-oncogenes. The transforming gene of ASV UR2, v-ros, its corresponding cellular gene, c-ros, and the proto-oncogene c-src will be studied. The functional domains of v-ros will be studied by constructing various site-specific mutants, and ros and src recombinants. Synthesis and subcellular location of the ros protein, its interaction with potential cellular substrates and transforming ability will be compared among parental UR2 and the mutants. The expression of c-ros gene in avian and mammalian tissues at various developmental stages will be examined at RNA and protein levels. The c-ros product will be identified and characterized using ros-specific antisera. In situ immunofluorescence will be performed to identify the specific cells in the tissue expressing the c-ros protein. The cDNA clone of c-ros mRNA will be constructed and sequenced to elucidate the complete c-ros product, which appears to mimic growth factor receptor molecules. To identify the sequence differences between c-ros and v-ros that may be responsible for the different transforming potential of the two genes, c-ros virus and c-ros recombinants will be constructed and compared with respect to their gene products and oncogenicity. Chicken c-src is known to direct the synthesis of a 4 kb mRNA which codes for a 60,000 dalton tyrosine-specific protein kinase. In muscle, while the 4 kb RNA is absent, a 3 kb c-src mRNA lacking most the kinase domain is expressed instead. Both the 4 kb and the 3 kb RNAs will be cloned and sequence to elucidate their nature of synthesis. The potential protein product of the 3 kb RNA will be identified by using antisera against peptides decoded from the nucleotide sequence. The role of this src- related protein in muscle development and function will be studied.